Disk drives place data in physical tracks based upon their logical track number. All access of this data occurs based upon the logical track number. Traditionally, disk drives with multiple read-write heads access successive data tracks, on their respective disk surfaces as illustrated in FIG. 2F. This mapping of logical track numbers to physical tracks is based upon a perception of how the read-write heads mechanically align to each other illustrated in FIG. 2E.
As Tracks Per Inch (TPI) in disk drives increase mechanical misalignments between these read-write heads have a significant impact on track seek time. These previously minor mechanical misalignments fail to match the perception illustrated in FIG. 2E, and lead to significant track seek time inefficiencies with the mapping scheme illustrated in FIG. 2F.
FIG. 1A illustrates a typical prior art high capacity disk drive 10 including actuator arm 30 with voice coil 32, actuator axis 40, actuator arms 50–58 and with head gimbal assembly 60 placed among the disks.
FIG. 1B illustrates a typical prior art, high capacity disk drive 10 with actuator 20 including actuator arm 30 with voice coil 32, actuator axis 40, actuator arms 50–56 and head gimbal assembly 60–66.
FIG. 2A illustrates a suspended head gimbal assembly 60 containing the MR read-write head 200 of the prior art.
Voice coil actuators including 20–66 are used to position read-write heads over specific tracks. The heads are mounted on head gimbal assemblies 60–66, which float a small distance off the disk drive surface when in operation. The air bearing is formed by the rotating disk surface 12, as illustrated in FIGS. 1A–1B, and slider head gimbal assembly 60, as illustrated in FIGS. 1A–2A.
Often there is one head per head slider for a given disk drive surface. There are usually multiple heads in a single disk drive, but for economic reasons, usually only one voice coil actuator.
Voice coil actuators are further composed of a fixed magnet actuator 20, interacting with a time varying electromagnetic field induced by voice coil 32, to provide a lever action via actuator axis 40. The lever action acts to move actuator arms 50–56 positioning head gimbal assemblies 60–66 over specific tracks with speed and accuracy. Actuators 30 are often considered to include voice coil 32, actuator axis 40, actuator arms 50–56 and head gimbal assemblies 60–66. An actuator 30 may have as few as one actuator arm 50. A single actuator arm 52 may connect with two head gimbal assemblies 62 and 64, each with at least one head slider.
Head gimbal assemblies 60–66 are typically made by rigidly attaching a slider 100 to a head suspension, including a flexure providing electrical interconnection between the read-write head in the slider and the disk controller circuitry. FIG. 2B illustrates the relationship between the principal axis 110 of an actuator arm 50 containing head gimbal assembly 60, which in turn contains slider 100, with respect to a radial vector 112 from the center of rotation of spindle hub 80 as found in the prior art.
The actuator arm assembly 50-60-100, pivots about actuator axis 40, changing the angular relationship between the radial vector 112 and the actuator principal axis 110. The farthest inside position is the Inside Position (ID). The position where radial vector 112 approximately makes a right angle with 110 is the Middle Position(MD). The farthest out position where the read-write head 100 accesses disk surface 12 is the Outside Position(OD). Crash Stop 90 is located near the Outside Diameter OD, and is discussed in FIG. 2D.
FIG. 2C illustrates a simplified schematic of a disk drive controller 1000 of the prior art, used to control an assembled disk drive 10.
Disk drive controller 1000 controls an analog read-write interface 220 communicating resistivity found in the spin valve within read-write head 200.
Analog read-write interface 220 frequently includes a channel interface 222 communicating with pre-amplifier 224. Channel interface 222 receives commands, from embedded disk controller 100, setting at least the read_bias and write_bias.
Various disk drive analog read-write interfaces 220 may employ either a read current bias or a read voltage bias. By way of example, the resistance of the read-write head is determined by measuring the voltage drop (V_rd) across the read differential signal pair (r+ and r−) based upon the read bias current setting read_bias, using Ohm's Law.
In FIG. 2C, channel interface 222 also provides a Position Error Signal PES to at least servo controller 240 may include a control feedback loop. The PES signal is used by servo controller 240 to control voice coil 32 to keep read-write head 200 close enough to a physical track 120 of FIG. 2B to support read-write head 200 communicatively accessing physical track 120.
FIG. 2D illustrates the prior art single level inertial latch mechanism including latch arm 230 pivoting about 232 and including latch hook 234, mechanically fitting with actuator catch mechanism 236, as well as latch stop 240, and crash stop 90, with the latch mechanism at rest. Note that actuator 30 abuts crash stop 90 and that inertial latch arm 230 abuts latch stop 240 when the single-lever inertial latch is at rest. Head gimbal assembly 60 is in position on parking ramp 250.
Each physical track, contains a successive graycode. The track under the crash stop 90 illustrated in FIGS. 2B and 2D, is also the Outside Diameter (OD), and has graycode number 0. Successive graycodes differ by exactly one bit. This is known as a hamming distance of one. A hamming distance of two indicates that two graycodes differ in exactly two bits.
FIG. 2E illustrates the prior art relationship between the read-write heads 200–0 to 200–3 and the tracks they access on the disk surfaces 12–18.
FIG. 2F illustrates the prior art logical track mapping to physical tracks. Until recently, tracks were far enough apart that the mechanical misalignment of read-write heads 200–0 to 200–3 as illustrated in FIG. 2E was negligible. The optimal mapping scheme for logical tracks to physical tracks in this situation is to have successive tracks on different head when possible as illustrated in FIG. 2F. This reduces the track seek problem to seeking within a fraction of a track width.
However, the inventors discovered that this situation is changing. As the TPI increases, the scenario illustrated in FIG. 2E no longer applies. As a consequence, the use of the mapping scheme for logical tracks of FIG. 2F is no longer optimal. What is needed is a new understanding of the relationship between read-write heads and tracks on disk surfaces, and better mapping schemes for logical tracks, which reflect the observed realities of contemporary and future high TPI disk drives. What is needed are methods of allocating logical tracks to physical tracks based upon these new insights.